1. Field of the Invention
The invention is an improved two-piece bicycle wheel rim having integral mating portions and improved composite layup providing lighter weight and increased strength in an economical manner without separate joining or reinforcing pieces.
2. Description of Related Art
Basic principles of optimum compaction low void composite molding the bicycle industry are described in U.S. Pat. Nos. 5,624,519 and 6,270,104, sharing a common assignee with this application. The disclosures in U.S. Pat. Nos. 5,624,519 and 6,270,104 are incorporated by reference as if fully set forth herein.
Metal wheel rims have long been made by bending a straight extrusion, bar or other shape to a circular form and then joining the ends to make a closed circle. Typical joining may include inserts such as U.S. Pat. No. 4,938,540, plugs of metal or even wood, or by welding as in European Patent Office Publication No. 0579525A1. These patents are incorporated by reference as fully set forth herein.
Owing to the different strength properties of composite fiber reinforced plastics, particularly the high tensile strength and high stiffness of materials such as carbon fiber, the base material is formed to shape prior to curing. Three typical methods of forming a wheel or wheel rim from carbon fiber reinforced plastic are known. These include a cored composite in which the high strength skin surrounds a core such a foam core, U.S. Pat. No. 5,061,013, a solid composite such as U.S. Pat. 6,347,839 B1 in which composite laminations have no designed end openings or different density materials between interior and exterior surfaces and a partially hollow but plugged construction such as U.S. Pat. No. 6,398,313 B1 where two hollow halves have interior inserts and exterior reinforcements at joining ends. The disclosures in these three patents are incorporated by reference as if fully set forth herein.
The invention avoids the drawbacks of the prior art using general principles of optimum compaction low void composite construction specially adapted to the unique shape and structural requirements of wheel rims using a combination of laminates incorporating fibers at different angles relative to one another, a curved auto-centering plug in one half at one end mating with a receptacle in an opposite, identical half further using unidirectional layers in key areas of the rim edges and spoke bed. A preferred embodiment further combines the preferred carbon fiber reinforced epoxy laminate structure with machinable and tough braking surface portions.